Is atheism a religion? Why or why not?

I umed atheism was a religion, since the Washington governor allowed atheists to juxtapose their display (an empty and insulting argument against theism) next to a manger scene at the capitol. In addition, atheists seem to make presuppositions akin to religious faith, e.g., statements about gods, angels, heaven, etc., expressed as certain dogmas. In addition, they evidence faith in scientific naturalism, that seems to reify some sort of secular designer (e.g., natural "selection"). Where am I going wrong?